Detachable magnetic holding devices are known such as from Levesque Patent No. 2,280,437, in which a rotatable permanent magnet assembly causes a pair of pole plates selectively to be magnetized or not magnetized, thereby selectively to attach or release the device relative to a magnetizable surface. This device has the inherent disadvantage that it can be attached only to a flat or prismatic surface.
An interesting attempt to adapt to a complex surface is shown in Walpole Pat. No. 1,171,818, in which pole plates of appropriate and different lengths are embedded in a structure so as to bear against electromagnetic poles at one end and against an irregularly shaped workpiece at the other. But this construction is a one-shot device suitable for only one shape. It is a single purpose construction, and is not an adaptable construction for accommodating to various shapes, one after another.
Yet another magnetic holding device is shown in Nagata Pat. No. 3,968,986, issued July 13, 1976. The Nagata device includes a series of adjacent electromagnets, each of which has a pair of poles that are rigidly fixed to one another. With this arrangement it is possible that only one pole piece at a time can contact the work. Unless the work is flat or prismatic the magnetic circuit is broken where one pole piece is spaced from the work because the other has made first contact. The device is therefore less effective.
It is an object of this invention to provide a simple and elegant magnetic holding device which can adapt to complex surfaces, making a completed magnetic circuit at both pole pieces, which relative to any surface can be aligned in various orientations.